This application is based upon, and claims the benefit of priority of, prior Japanese Patent Application 2001-175972, filed on Jun. 11, 2001, the contents of which are incorporated herein by reference.
1. Technical Field of the Invention
The present invention relates to a vehicle head lamp utilizing a discharge lamp.
2. Description of Related Art
Generally, discharge lamps are used as vehicle head lamps. The discharge lamp is an arc-discharge type lamp in which xenon gas, or the like, is enclosed in a discharge lamp bulb (arc tube), and light is emitted from the discharge lamp bulb using discharge generated between a pair of electrodes therein. The light emitted from the discharge lamp bulb is white light similar to sun light. A quantity of light from the discharge lamp can be equal to or more than twice as much as that from a conventional halogen lamp while using about 30% of the electric power compared to the halogen lamp. Accordingly, when the discharge lamp is used as a vehicle head lamp, visibility in front of the vehicle is improved.
When the discharge lamp is turned on, a high voltage of several kV to tens of kV is applied to the discharge lamp, thereby instantly starting discharge therein, and lighting it. Thereafter, electric power of about 35W is applied to maintain a lit condition. Therefore, a dedicated lighting-control circuit is required to light the discharge lamp. A lighting control circuit is mainly constructed by a converter, an inverter and an igniter. The converter increases the direct-current (DC) voltage from a battery, and the inverter converts a DC voltage to an alternating-current (AC) voltage. The igniter generates a high voltage of tens of kV.
In a vehicle, the lighting control circuit is generally mounted outside the head lamp housing. In this case, high voltage wires and connectors, used for applying a high voltage to the discharge lamp, are required, thereby not reducing the size of the head lamp and its peripheral circuit. Further, labor hours for attachment and wiring of the high voltage wires and connectors are required while a certain amount of space for the wires and the connectors is required. Furthermore, the high voltage wire requires shielding for reducing adverse effects of electrical noises from the wire itself, thereby increasing production costs of the head lamp and its peripheral circuit.
Therefore, it can be considered that the lighting control circuit is mounted directly on the discharge lamp bulb in the lamp housing. For example, it is conceived that the discharge lamp bulb is connected directly to a connector contained in the lighting control circuit while the lighting control circuit is fixed to a rear surface of a reflector. According to this arrangement, no high voltage wire is required between the discharge lamp bulb and the lighting control circuit while the size of the vehicle head lamp can be reduced, thereby eliminating radio wave noises and power losses due to the high voltage wires.
While the discharge lamp bulb is lit, its temperature becomes high. Generally, ventilation holes are provided in the lamp housing to eliminate any pressure differences between the inside and the outside of the lamp housing. However, the area of each ventilation hole is set at a desired minimum to prevent water and foreign matter from entering into the lamp housing, which causes almost no air stream is generated in the lamp housing. Therefore, while the discharge lamp bulb is lit, the air temperature in the lamp housing becomes high. That is, a temperature of the lighting control circuit becomes high by receiving heat directly from the discharge lamp bulb through thermal conduction and thermal radiation while the temperature of air around the lighting control circuit becomes high. Thus, it is feared that excessive thermal loads may be applied to circuit elements contained in the lighting control circuit. Although circuit elements and a circuit board, each having a high thermal resistance, may be used as one remedy for this problem, production costs and the size of the lighting control circuit will increase.
As another remedy, the lamp housing may define an opening, and a portion of the lighting control circuit fixed to the reflector may be exposed to the outside through the opening in the lamp housing. Thus, the lighting control circuit is cooled using outside air, and its temperature is prevented from increasing. In this case, a sealing member is required to close a clearance between the lighting control circuit and the lamp housing at the opening which exposes the lighting control circuit to seal the lamp housing.
In attachment processes of the vehicle head lamp, an optical axis is adjusted by moving the reflector. Further, some vehicle head lamps include a leveling mechanism. In the leveling mechanism, when vehicle posture (position) changes due to changes in passenger arrangement or changes in the load condition, the optical axis of the head lamp is maintained in a predetermined direction by moving the reflector through the use of a motor or an actuator. A clearance varies between the lighting control circuit and the lamp housing on every vehicle head lamp due to driving conditions. Therefore, the clearance therebetween is difficult to securely seal.
The present invention has been made in view of the above problems. An object of the present invention is to provide a vehicle head lamp so the temperature of the lighting control circuit can be effectively prevented from increasing. That is, a portion of the lighting control circuit fixed to the reflector is exposed outside the lamp housing while the lamp housing remains hermetically sealed regardless of the posture of the reflector. Thus, a temperature of the lighting control circuit can be effectively prevented from increasing by using outside air.
In the present invention, the following technological means are adopted to attain the above object. A lamp housing defines an opening at a side of a lighting control circuit. An end portion of the lighting control circuit is exposed to an exterior by the opening in the lamp housing. Further, a seal member is formed by a flexible material substantially in an annular shape, and an outer circumferential portion of the seal member is tightly fixed to the lamp housing around a peripheral portion of the opening. An inner circumferential portion of the seal member is tightly fixed to or press-contacted to the lighting control circuit at a peripheral side of its end portion. Thus, since the seal member can be deformed to adjust to posture changes of the reflector, the lighting control circuit can be cooled using an outside air stream while the lamp housing is surely sealed. That is, a portion of the lighting control circuit fixed to the reflector is exposed outside the lamp housing. Therefore, the temperature of the lighting control circuit can be prevented from increasing, and thermal loads applied to circuit elements can be reduced or maintained.
The vehicle head lamp further includes an actuator for moving the reflector. Accordingly, when vehicle posture (position) change due to changes in passenger arrangement within the vehicle and/or changes of the vehicle""s load condition, the optical axis of the head lamp is maintained in a predetermined direction by moving the reflector using an actuator (leveling mechanism). Also in the vehicle head lamp, a portion of the lighting control circuit fixed to the reflector is exposed outside the lamp housing and the lighting control circuit can be cooled using an outside air stream. Therefore, the temperature of the lighting control circuit can be prevented from increasing, and thermal loads applied to circuit elements can be reduced.
Additionally, the vehicle head lamp may include a heat radiation member formed by a high thermal-conduction material. The heat radiation member is fixed to the lighting control circuit and the seal member is tightly fixed to or press-contacted to the heat radiation member. Therefore, an outer circumferential shape of the heat radiation member is optimized to improve adhesion between the heat radiation member and the seal member, thereby securely sealing the lamp housing. Additionally, the lighting control circuit includes heat radiation fins exposed by the opening to the lamp housing exterior. Therefore, the lighting control circuit can be effectively cooled using an outside air stream. Also, a seal member is constructed by a plurality of components. Therefore, an inner circumferential shape of the seal member is optimized to improve adhesion between the lighting control circuit and the seal member, thereby securely sealing the lamp housing.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.